java设计模式

15.观察者模式：购物网站上用户添加到货通知后，商品有货后，就会主动通知订阅到货通知的用户

public interface Observer {
public void update();
}

public class Observer1 implements Observer {
public void update() {
System.out.println("Observer1 has received notify");
}
}

public class Observer2 implements Observer {
public void update() {
System.out.println("Observer2 has received notify");
}
}

对用户操作接口：

public interface Subject {
public void add(Observer observer);
public void del(Observer observer);
public void notifyAllObservers();
public void operation();
}

public class AbstractObserver implements Subject {
private Vector<Observer> vector = new Vector<Observer>();

public void add(Observer observer) {
vector.add(observer);
}

public void del(Observer observer) {
vector.remove(observer);
}

public void notifyAllObservers() {
Iterator<Observer> iterator = (Iterator<Observer>) vector.iterator();
while (iterator.hasNext()) {
Observer observer = iterator.next();
observer.update();
}
}

public void operation() {
//To change body of implemented methods use File | Settings | File Templates.
}
}

实现类：

public class MySubject extends AbstractObserver {
public void   operation(){
notifyAllObservers();
}
}

public class Test {
public static void main(String[] args) {
Subject subject = new MySubject();
subject.add(new Observer1());
Observer2 observer2=new Observer2();
subject.add(observer2);
subject.operation();
System.out.println("=============");
subject.del(observer2);
subject.operation();

}
}

如果要增加其他通知类型，可以在Observer接口新增方法，例如消息推送，

16.迭代器模式：先顺序访问对象，再对对象中元素遍历访问，例如Iterator ite=Collection.iterator ite.hasNext();

public interface Iterator {
public Object previous();
public Object next();
public boolean hasNext();
public Object first();
}

public interface Collection {
public Iterator iterator();
public Object get(int i);
public int size();
}

Collection中可以获取Iterator

public class MyCollection implements Collection {
String[] strings = {"a","b","c"};
public Iterator iterator() {
return new MyIterator(this);  //To change body of implemented methods use File | Settings | File Templates.
}

public Object get(int i) {
return strings[i];  //To change body of implemented methods use File | Settings | File Templates.
}

public int size() {
return strings.length;  //To change body of implemented methods use File | Settings | File Templates.
}
}

public class MyIterator implements Iterator {
private int pos = -1;
private Collection collection;

public MyIterator(Collection collection) {
this.collection = collection;
}

public Object previous() {
if (pos > 0) {
pos--;
}
return collection.get(pos);  //To change body of implemented methods use File | Settings | File Templates.
}

public Object next() {
if (pos < collection.size() - 1) {
pos++;
}
return collection.get(pos);  //To change body of implemented methods use File | Settings | File Templates.
}

public boolean hasNext() {
if (pos < collection.size() - 1) {
return true;
}
return false;
}

public Object first() {
if (collection.size() > 0) {
return collection.get(0);
}
return null;
}
}

测试类：

public class Test {
public static void main(String[] args) {
Collection collection = new MyCollection();
Iterator iterator = collection.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}

}
}

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